1. Field of the Invention
This invention is generally directed to antennas and more specifically to wire or rod type antennas which are directional and which are specifically designed to focus receipt of signals from predetermined areas such that the vertical and horizontal extent of the signals being received can be regulated to prevent bleed such as from one floor to another in a multi-level building or structure.
2. History of Related Art
Radio frequency identification systems are well known for object and personnel tracking, surveillance, inventory control and the like wherein either active or passive RFID tags are placed on objects or personnel to be monitored. Each tag is provided with a unique code which, if passive, is activated upon the receipt of radio frequency (RF) energy to reflect a signal to a detector which signal carries a unique signature for the tag. In an active tag system the tag also carries unique information, however, the information is periodically broadcast to a detector or sensor mounted in a remote location through energy supplied by a battery associated with the active tag. The timing of the lumination of energy from the tag can be built into the tags during their manufacture. In some RFID systems, tags can be used having both active and passive characteristics.
It is often desirable to use RFID systems in multi-level confined areas such as within multi-floored buildings including warehouses, hospitals, manufacturing facilities and the like to monitor various equipment, articles, supplies and the like which are present. By way of example, in a hospital setting, there is important equipment which must be readily available and its location known at all times. By placing an RFID tag on such equipment and providing appropriate sensors within the hospital environment, the current location of the equipment is always known. In some instances, monitoring can be provided to prevent theft as well as to insure for inventory control. Further, some equipment, especially in hospitals, should not be moved out of certain protected environments such as equipment utilized for X-Ray purposes and the like. By monitoring tags associated with such equipment, it is possible to ensure that the equipment is maintained in a safe and controlled environment at all times.
RFID systems which are currently in use generally operate either using omnidirectional transceivers, for passive tag systems, or receivers, for active tag systems. The omnidirectional nature of the transceivers or receivers is predicated upon the configuration of the antennas which are used for broadcasting or receiving radio frequency signals.
Generally each tag of a passive or an active system is designed to operate at a generally specific frequency which frequency may be chosen to suit a particular environment. That is, the frequency is chosen so as not to interfere with other radio frequency equipment which may be located within a facility or in the environment of the RFID tag system. Currently, systems are designed which operate both at high frequency wavelengths as well as relatively low frequency wavelengths.
One problem that has resulted with RFID monitoring systems is that often tags outside a given detection zone can be detected by a transceiver or receiving antenna. Thus the antenna may supply false signals to an analyzer or detector device which is monitoring objects within a given area. By way of example, in a multistory building using conventional transceiver and receiving omnidirectional antenna structures, signals are often received from passive or active tags from objects which are located at levels above or below a given floor on which a detector or sensor is mounted. When bleed-over signals are received, it is possible that a false location of a particular object will be provided to the operators of the tag system because an article is on or located at a different vertical location than predicted by the sensors.
With conventional systems utilizing the omnidirectional antenna transceivers or receivers, it has generally been the practice to utilize transceivers or receiving antennas which are electrically connected to control readers or the like such that a fields of coverage of the antennas overlap one another to give as complete a coverage to the area being monitored as is possible. Unfortunately, overlapping not only occurs through a horizontal beam width of any signal being transmitted or received but also vertically. In view of the foregoing, it is often necessary to provide additional control equipment so that a true location can be determined for RFID tags by comparing the various signals being received at each location to determine signal strengths both in a vertical and horizontal direction to identify the probable location of the tags detected. This results in duplication of detection and antenna equipment thereby elevating the costs of such systems.
As described, in radio frequency identification systems which are utilized in enclosed environments including multiple level structures, there is often a bleed-over of RF frequencies being generated from tagged objects from one floor to another. To avoid confusion and to accurately locate objects, it is often necessary to place secondary sensors or signal generators at different locations along each floor of the building which provide specific information as to the location of the signal generators within the structure. The signals generated can be received by antennas and processed in order to determine a signal strength that should be received from a specific location. This requires that hardware and software be provided for the operating system so that the system is able to differentiate the signals being received depending upon the strength of the signals and angle or direction of the signals being received. Such signals, however, are affected by the types of building material being used within a structure, such as within the walls of the structure or in the floors of the structure, which materials affect the signals. By using known signal generators, when signals are received from the tags placed throughout the structure, the computing software can differentiate between the various locations. Placing known location signal generators throughout a structure increases the overall cost and complexity of an RFID system and makes such monitoring systems prohibitively expensive for use in many environments.
A zone based radio frequency identification system is described in U.S. Pat. No. 6,552,661 to Lastinger et al., the contents of which are incorporated in their entirety by reference. The system provides for determining whether or not identification devices, such as RF tags, are located within a particular zone. Therefore, a building is divided into separate zones and the zones are determined by providing different locator signals within each zone to establish boundary levels for signals. In this manner, by comparing the signals from predetermined placed devices, it can be determined when a tag being monitored is within a particular zone.
In view of the foregoing, there is a need to provide for antennas for use with transceivers or receiving type antennas utilized with RFID tag systems which can be used to specifically monitor tagged objects on a specific floor of a multistory building or structure without receiving bleed-over signals from adjacent floors and further to provide such systems wherein substantially all areas of a given floor are effectively covered by the radio frequency receiving antennas to ensure that an object can be located regardless of its position along a specific floor utilizing a minimum number of receiving and/or transceiver antennas.